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AP Biology 2007-2008 Control of Eukaryotic Genes.

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Presentation on theme: "AP Biology 2007-2008 Control of Eukaryotic Genes."— Presentation transcript:


2 AP Biology Control of Eukaryotic Genes

3 AP Biology The BIG Questions… How are genes turned on & off in eukaryotes? How do cells with the same genes differentiate to perform completely different, specialized functions?

4 AP Biology Evolution of gene regulation Prokaryotes single-celled evolved to grow & divide rapidly must respond quickly to changes in external environment exploit transient resources Gene regulation turn genes on & off rapidly flexibility & reversibility adjust levels of enzymes for synthesis & digestion

5 AP Biology Evolution of gene regulation Eukaryotes multicellular evolved to maintain constant internal conditions while facing changing external conditions homeostasis regulate body as a whole growth & development long term processes specialization turn on & off large number of genes must coordinate the body as a whole rather than serve the needs of individual cells

6 AP Biology Points of control The control of gene expression can occur at any step in the pathway from gene to functional protein 1.packing/unpacking DNA 2.transcription 3.mRNA processing 4.mRNA transport 5.translation 6.protein processing 7.protein degradation

7 AP Biology How do you fit all that DNA into nucleus? DNA coiling & folding double helix nucleosomes chromatin fiber looped domains chromosome from DNA double helix to condensed chromosome 1. DNA packing

8 AP Biology Nucleosomes Beads on a string 1 st level of DNA packing histone proteins 8 protein molecules positively charged amino acids bind tightly to negatively charged DNA DNA packing movie 8 histone molecules

9 AP Biology DNA packing as gene control Degree of packing of DNA regulates transcription tightly wrapped around histones no transcription genes turned off heterochromatin darker DNA (H) = tightly packed euchromatin lighter DNA (E) = loosely packed H E

10 AP Biology DNA methylation Methylation of DNA blocks transcription factors no transcription genes turned off attachment of methyl groups (–CH 3 ) to cytosine C = cytosine nearly permanent inactivation of genes ex. inactivated mammalian X chromosome = Barr body

11 AP Biology Histone acetylation Acetylation of histones unwinds DNA loosely wrapped around histones enables transcription genes turned on attachment of acetyl groups (–COCH 3 ) to histones conformational change in histone proteins transcription factors have easier access to genes

12 AP Biology 2. Transcription initiation Control regions on DNA promoter nearby control sequence on DNA binding of RNA polymerase & transcription factors base rate of transcription enhancer distant control sequences on DNA binding of activator proteins enhanced rate (high level) of transcription

13 AP Biology Model for Enhancer action Enhancer DNA sequences distant control sequences Activator proteins bind to enhancer sequence & stimulates transcription Silencer proteins bind to enhancer sequence & block gene transcription Turning on Gene movie

14 AP Biology Transcription complex Enhancer Activator Coactivator RNA polymerase II A B F E H TFIID Core promoter and initiation complex Activator Proteins regulatory proteins bind to DNA at distant enhancer sites increase the rate of transcription Coding region T A Enhancer Sites regulatory sites on DNA distant from gene Initiation Complex at Promoter Site binding site of RNA polymerase

15 AP Biology 3. Post-transcriptional control Alternative RNA splicing variable processing of exons creates a family of proteins

16 AP Biology 4. Regulation of mRNA degradation Life span of mRNA determines amount of protein synthesis mRNA can last from hours to weeks RNA processing movie

17 AP Biology RNA interference Small interfering RNAs (siRNA) short segments of RNA (21-28 bases) bind to mRNA create sections of double-stranded mRNA death tag for mRNA triggers degradation of mRNA cause gene silencing post-transcriptional control turns off gene = no protein produced NEW! siRNA

18 AP Biology Action of siRNA siRNA double-stranded miRNA + siRNA mRNA degraded functionally turns gene off Hot…Hot new topic in biology mRNA for translation breakdown enzyme (RISC) dicer enzyme

19 AP Biology RNA interference 1990s | 2006 Andrew Fire Stanford Craig Mello U Mass for their discovery of RNA interference gene silencing by double-stranded RNA

20 AP Biology 5. Control of translation Block initiation of translation stage regulatory proteins attach to 5' end of mRNA prevent attachment of ribosomal subunits & initiator tRNA block translation of mRNA to protein Control of translation movie

21 AP Biology 6-7. Protein processing & degradation Protein processing folding, cleaving, adding sugar groups, targeting for transport Protein degradation ubiquitin tagging proteasome degradation Protein processing movie

22 AP Biology Ubiquitin Death tag mark unwanted proteins with a label 76 amino acid polypeptide, ubiquitin labeled proteins are broken down rapidly in "waste disposers" proteasomes 1980s | 2004 Aaron Ciechanover Israel Avram Hershko Israel Irwin Rose UC Riverside

23 AP Biology Proteasome Protein-degrading machine cells waste disposer breaks down any proteins into 7-9 amino acid fragments cellular recycling play Nobel animation

24 AP Biology initiation of transcription 1 mRNA splicing 2 mRNA protection 3 initiation of translation 6 mRNA processing 5 1 & 2. transcription - DNA packing - transcription factors 3 & 4. post-transcription - mRNA processing - splicing - 5 cap & poly-A tail - breakdown by siRNA 5. translation - block start of translation 6 & 7. post-translation - protein processing - protein degradation 7 protein processing & degradation 4 4 Gene Regulation

25 AP Biology Turn your Question Genes on!

26 AP Biology & 2. _________________ - ____________________ 3 & 4. _________________ - ____________________ 5. _________________ - ____________________ ____________________ 6 & 7. _________________ - ____________________ Gene Regulation

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